The present invention relates generally to valve assemblies, and more particularly to valve assemblies for a homogenous charge compression ignition engines.
A common method of achieving homogenous charge compression ignition is to include at least one fuel injector that injects fuel into its respective engine cylinder when the cylinder piston is relatively far from a top dead center position during a compression stroke. The fuel then mixes with air in the cylinder during the compression stroke to form a relatively lean homogeneous fuel/air mixture. For certain engine operating conditions, this type of engine operation can result in combustion that produces less undesirable emissions than typical diesel engine operation. However, it should be appreciated that, because the injected fuel does not immediately ignite, timing of the ignition during homogenous charge compression ignition engine operation is critical. In other words, it is desirable that the ignition event occur when the cylinder piston reaches or nears the top dead center position for its compression stroke. When the start of ignition occurs too soon, the fuel and air mixture will burn during the compression stroke of the cylinder piston, resulting in possible engine damage and poor cycle efficiency. In addition, this could lead to high temperatures during the next engine cycle, which could result in another early start of ignition.
Numerous attempts have been made to control ignition timing for homogenous charge compression ignition engines. For example, one such attempt is described in U.S. Pat. No. 5,832,880, which issued to Dickey on Nov. 10, 1998, and is entitled Apparatus And Method For Controlling Homogenous Charge Compression Ignition Combustion In Diesel Engines. In Dickey, a closed loop control strategy is disclosed which includes regulation of the ignition timing via an amount of water that is injected into a cylinder of a homogenous charge compression ignition engine. While this purported solution may have some viability, there is still room for improvement. For instance, for those engines that do not utilize water-spraying fuel injectors, a solution to controlling timing of ignition events and duration of the combustion events is needed.
The present invention is directed to overcome one or more of the problems as set forth above.
In a first aspect of the present invention, a homogenous charge compression ignition engine includes an engine housing that defines a plurality of engine cylinders, wherein each of the plurality of engine cylinders includes a moveable piston that reciprocates between a top dead center position and a bottom dead center position. A fuel injector is provided for each engine cylinder and is operable to inject fuel into the engine cylinder when the piston is closer to the bottom dead center position than the top dead center position. At least one intake valve is provided for each said engine cylinder. A cam is sized and positioned such that it can mechanically engage the at least one intake valve. An electro-hydraulic assist actuator is able to mechanically engage the at least one intake valve.
In another aspect of the present invention, a method of operating an engine includes a step of injecting fuel into an engine cylinder when a cylinder piston is closer to a bottom dead center position than a top dead center position. At least one gas exchange valve is held open, at least in part by a rotating cam mechanically engaging the at least one gas exchange valve. Ignition timing is adjusted, at least in part by actuating an electro-hydraulic assist actuator that is able to mechanically engage the at least one gas exchange valve.
In yet another aspect of the present invention, a valve assembly includes at least one gas exchange valve. A rotating cam is provided that is mechanically engageable with the at least one gas exchange valve. An electro-hydraulic assist actuator is provided that includes a movable plunger and is capable of engaging the at least one gas exchange valve.